In the petroleum industry oil and gas recovery operations use significant amounts of water that can be contaminated by bacteria and in many cases endospores. Some non-limiting examples of applications that use said water include: well drilling, hydraulic fracturing, desalination for the removal of accumulated salts from down-hole artificial lift pumps; water flooding to displace more petroleum in the geologic formation toward the collection well, and power fluid used for operating jet pumps to extract formation fluids.
Many bacteria are facultative, that is they can exist in aerobic or anaerobic conditions using either molecular oxygen or other oxygen sources to support their metabolic processes. For example, under the right conditions, facultative bacteria can use sulfate as an oxygen source and respire hydrogen sulfide, which is highly toxic to humans in addition to being corrosive to steel. Additionally, in a process known in the art as Microbiologically Induced Corrosion (MIC), bacteria will attach to a substrate, such as the wall of a pipe in the wellbore, and form a “biomass” shield around them. Underneath, the bacteria metabolize the substrate (e.g. a mixture of hydrocarbon and metallic iron) and respire hydrogen sulfide, resulting in the metal becoming severely corroded in the wellbore and, eventually, pipe failure and damage to down-hole equipment. The respiration and presence of hydrogen sulfide also complicates the refining and transportation process, and attenuates the economic value of the produced hydrocarbon.
The traditional methods, when used alone to address these problems, have one or more drawbacks. For example, the present industry practice is to add conventional organic and inorganic biocides, such as quaternary ammonium compounds, chloramines, aldehydes, such as Gluteraldehyde, THPS and sodium hypochlorite, to fracturing fluids with other additives to control bacteria. The efficacy of these conventional biocides alone, however, can be minimal due to the type of bacteria that typically are found in hydrocarbon-bearing formations and petroleum production environments. More particularly, only a small percentage of these bacteria, which are often found in volcanic vents, geysers, and ancient tombs, are active at any one time; the remainder of the population is present in dormant and spore states. The aforementioned conventional biocides have no, or limited, effect on dormant and spore forming bacteria. Thus, while the active bacteria are killed to some extent, the inactive bacteria survive and thrive once they reach the environmental conditions found within the formation. Additionally, these biocides become inactivated when exposed to many of the components found in petroleum production formations. And, furthermore, microorganisms build resistance to these biocides, thus limiting their utility over time.
Chlorine dioxide, on the other hand, can inactivate active, dormant (endospores) and spore forming microorganisms at comparatively low concentrations (e.g. 10 ppm). Unlike conventional biocides, microorganisms do not build a resistance to chlorine dioxide. Chlorine dioxide is also selective compared to indiscriminate oxidizing biocides like bromine and chlorine. Chlorine dioxide is therefore an efficacious biocide however certain applications have not been possible prior to the invention. For example, producing wells often require desalination of the down-hole pumps (lift-jacks) to remove the mineral salts that accumulate and foul the pump. Producing wells are located in remote areas where the limited attention and access makes the use of chlorine dioxide unpractical and potentially dangerous.
The dangers of chlorine dioxide are well known to those skilled in the art. Chlorine dioxide vapors have caused explosions causing severe damage, injuries and even death. Referring to U.S. Pat. No. 4,013,761, Ward et al. discloses the concerns associated with chlorine dioxide vapors and its inherent danger.
In order to be able to provide wide-spread application of chlorine dioxide to treat these applications, a method and system are needed that provides for the autonomous generation of chlorine dioxide that is inherently safe, due to its self-limiting generating capacity.
In one embodiment, a method is disclosed that provides for the autonomous generation of safe self-limiting concentrations of chlorine dioxide.
In another embodiment, a method is disclosed for the autonomous generation of safe self-limiting concentrations of chlorine dioxide for the treatment of process water used in hydrocarbon recovery applications.
In another embodiment, a method is disclosed for the autonomous generation of safe self-limiting concentrations of chlorine dioxide for the treatment of process water used in an aquatic facility.
In another embodiment, a method is disclosed for the autonomous generation of safe self-limiting concentrations of chlorine dioxide for the treatment of industrial cooling water.
In yet another embodiment, a method is disclosed for the autonomous generation of safe self-limiting concentrations of chlorine dioxide for the treatment of waste water.